Rotor blade



May 1o, 1949.d

c. M. sEl'BEl.

ROTOR BLADE 3 Sheets-Sheet 1 d I I n n I n r I n r I 1 l I Jll I Filed Oct. 23, 1946 C. M. SEIBEL Roman BLADE May l0, 1949.

3 Sheets-Sheet 2 Filed ct. 2s, '194s Y lnvenor Chcjr/es /\1. .Se/be] 1.55

Patented May 10, 1949 ROTOR BLADE Charles M. Seibel, Kenmore, N. Y., asslgnor, to Bell Aircraft Corporation, Wheatfleld, N. Y.

Application October 23, 1946, Serial No. 705,203

This invention relates to rotors and more par-V time maintaining the overall weight within apermissible range.

Another object of the invention is -to provide an improved light weight rotor blade construction embodying an improved dynamic stability feature whereby to reduce weaving tendencies therein.

Another object of the invention is to provide an improved form of composite wood construction in a rotor blade.

Another object of the invention is to provide an improved form of composite wood and surface-armored rotor blade construction for rotary wing aircraft.

Other objects and advantages of the invention will appear from the specication hereinafter.

In the drawings:

Fig. 1 is a top plan view of a rotor blade of the invention;

Fig. 2 is a horizontal section through the blade ol Fig. l;

Fig. 3 is a top plan view of the rotor blade of Fig. 1 with the outer covering and a top plywood layer thereof removed;

Fig. 4 is a top plan view similar to Fig. 3 except that only the outer covering is removed;

Fig. 5 is a chordwise section, on an enlarged scale, at line V-V of Fig. 1;

Fig. 6 is a fragmentary section, on an enlarged scale, at line VI-VI of Fig, 1; Y

Fig. '7 is a fragmentary section, on an enlarged scale, at line VII-VII of Fig. 1;

Fig. 8 is a section, on an enlarged scale, at line VIII-VIII; and

6 Claims. (Cl. 17o-159).

Fig. 9 is a fragmentary typical sectionof the blade, showing the leading edge covering device thereof in disassembled relation, to illustrate the mode of fabrication of the blade.

The invention contemplates a novel rotor blade construction comprising a special truss-like construction interiorly of the blade so as to provide a light weight blade having in combination, a

maximum forward position of the center of gravity of the entire blade structure, and improved chordwise rigidity against bending. It hasbeen determined by extensive research that much of the previous difllculty with rotor vibrations at low airspeeds has resulted from the fact that' prior type light weight rotor blades possess relatively low bending frequencies in chordwise direction, and that therefore under transverse airflow conditions such blades tend to couple in a vibratory manner with other portions of the aircraft to create'extreme flight vibration ^iects. Also, it is known that by moving the location of the chorwise center of gravity of the blade forwardly produces anti-weaving tendencies.

Previously attempted solutions of the above stated problems in connection with the use of relatively long and slender rotor blades constructed of wood materials have involved increasing the rigidity of such blades against chordwise bending by tapering the -blades or otherwise reinforcing them by means and methods which have tended to unduly increase the weight of the blades as well as theV complexity of the manufacturing problems.

The present invention contemplates solution of the above stated problems by constructing the blade to include interiorly thereof a special beamlike structure which is formed of relatively strong woods; the beam structure having spaced flange portions which are Strong in tension-compression at the leading and trailing edges of the blade, and a web portion or portions disposed chordwise of the blade and interconnecting said anges so as to give the blade rigidity against chordwise bending, although the beam structure is of lighter total weight than the usual type laminated wood rotor. The outer contour of the blade is then provided by simply padding the beam structure with extremely light weight filler material such as balsa wood and enclosing the fabrication with a weather-sealing covering. The relatively heavy wood portions of the structure are dimensioned and positioned so as to dispose the overall center of gravity and the elastic axis of the blade structure further forwardly than in the usual case and hence toward the ideal position thereof.

More specically, and by way of an example of the invention, a blade is shown in the drawing to include a beam-like structure comprising a leading edge iiange portion Ill formed of lamiof the rotor blade. The birchwood plates are l3 lockedtogether by suitable cement such as a plastic cement, and a steel plate l2 ls embedded within the .birchwood portion I in close proxlmity to the front edge thereof to extend throughout the length of the blade and to terminate adjacent the root end of the blade in an enlarged eye portion 14. The eye portion I4 is in registry with vertical borlngs through the wood portions of the blade structure so as to be adapted to receive therethrough a bolt or pin (not shown) for connection to .the rotor hub. A collar l5 (Fig..8) is preferably built intol the blade root end to provide a suitable bearing for the hub connection bolt or pin. Thus, it will be understood that the steel plate l2 will be linked directly to the hub connection so as` to transmit thereto centrifugal loads under operative conditions, and that the forward location of the plate I2 within the leading edge portion of the blade structure will assist in bringing forward the center of gravity of the entire bladestructure.

The trailing edge flange portion of the beam construction may be provided as illustrated in the drawing in the form of a laminated spruce wood formation designated 20; comprising spruce wood plates disposedl vertically edgewise and extending lengthwise in the spanwise directionof the rotor blade and locked together by suitable cement such as referred to hereinabove. Preferably, the spruce wood formation 20 is disposed at the extreme trailing edge portion of the blade so as to be spaced the maximum permissible distance from the front plate structure i6, although in the region of the root end of the blade it is preferred to form the plate portion 20 with a forwardly extending portion 2l directly cemented to the front birch wood plate element IE. Thus, the birch wood and spruce wood members lll- 20 will cooperate to provide a blade root structure which is formed solidly of relatively strong woods leading into the beam-type formation referred to hereinabove.

The plate element 2li may be conveniently designed of `bifurcated planform so as to previde a front edge portion 22 for cemented connection directly to the front plate I0 and a trailing edge portion spaced rearwardly thereof, in addition to the solid root end portion 2|. space between the trailing edge portion 20 and the front edge portion 22 of the spruc'e wood formation is preferably filled with a suitable light weight substance, such as a tongue-shaped balsa wood piece indicated at 23. As shown in Figs. 2-3-4, the balsa wood formation 23 is preferably constructed by cementing a series of balsa wood 'blocks together in laminated form with the gain of the wood running chordwise of the blade and lengthwise of the balsa wood blocks so that the end grain portions of the balsa wood blocksgare disposed in abutting relation against the birch wood and spruce wood portions lli- 20.

To reinforce the cemented juncture between the birch wood element I0 and the balsa wood filler element 23, I prefer to overlap the juncture both at' the top and the bottom surfaces of the blade by means of hard plywood strips 2li-26, respectively; the balsa and birch wood elements being suitably recessed to receive the plywood strips in cemented relation thereon. The front and rear beam portions IIL-2U are interconnected, as contemplated by the invention by means of one or more web members formed or relatively strong wood; and as illustrated herein the web members are supplied in the form of plywood elements spanning the space between The ' the prescribed alignment.

the plates `lla-za boni at the top and at the and overall weight considerations, and it has been determined that it is not required that the spruce wood portion 20 extend as far as-the blade tip. but willpreferably terminate in the region of the mid span of the blade as indicated at 32A (Fig. 3)4 thereby reducing the weight of the tip end portion of the blade and helping to keep'` the chordwise center of gravity of the outboard end portion of the blade forwardly in proximity with the average position of the center of pressure'thereon. The .birch wood and spruce wood and balsa wood and plywood portions of the blade structure are cemented together as explained hereinabove by any suitable wood' cementing orglue material,l and the composite structure is exteriorly shaped so vas to provide the desired airfoil contouring thereof. The structure is then'preferably covered by a woven glass thread fabric which is cemented thereto as indicated at 35. This type of cover has the ,advantages of extreme durability and resistance to weathering, as well as being non-shrinkable and therefore not subject to pulling subsequent to application to the wood structure such as .would otherwise tend to warp the blade out of The leading edge portion of the blade is preferably armored as by means of a sheet metal lU-shaped covering plate 36 which is preformed.

to embrace the leading edge portion of the blade and to be adapted to be slip-fitted thereover subsequent to application of the fabric covering 35. Hence', the nose plate 36 overlies the front edge i portions of the Icovering 35 and clamps the latter into firm connection with the blade structure. Wood screws or the like as indicated at 38 (Figs. 5 6-7) may be employed to lock the nose plate and plywood sheet elements together with the birch wood structure I0. An anchor plate of metal or the like as indicated at 40 may be fixed Ato the root-end of the blade structure to take the bearing loads at the points of connection to the rotor hub and'blade angle control devices.

More specifically, the `'drawing illustrates thev beam Web elements to comprise at the upper surface portion of the blade a plywood member 2t, and at the lower surface of the blade a plywood member 30; the plywood members 28-30 being of similar shapes and dimensions in plan view. However, it is to be understood Athat the plywood web portion or portions of the beam construction may be disposed at any other desired elevation within the blade structure, in lieu of being dis# posed at the top and bottom surfaces thereof as illustrated hereinabove. For example, the plywood element might be disposed centrally of the blade section'proflle, with filler blocks of balsa at opposite sides thereof to complete the blade contour. In such case an I-beam structure would exist insteadof the box beam construction illustrated and described hereinabove; but it is thought that the box beam type construction is v s to be preferred because of its greater resistance to torsional twisting.

The novel beam-like construction comprising the relatively strong wood elements Ill- 2 l12 I 22 and the web elements 28-30 cooperate to reinforce the overall blade structure so as to raise the frequency of the blade in tension and compression against chordwise bending of the blade in plan view; and by reason of this novel blade construction the above stated feature is obtained in combination with a reduction in total blade weight, and dispositioning of the blade center of gravity and elastic axis forwardly toward the ideal positions-l thereof. It has been confirmed by tests that the trailing edge strong wood portion 2U need not extend entirely to the tip end of the blade in order to provide the chordwise stiffness feature referred to hereinabove; and that by terminating the portion as at the position designated 32, the overall center of gravity of the blade will be thereby moved forwardly.

It is of course to be understood that although only one form of blade of the invention has been shown and described in detail herein it will lbe apparent to those skilled in the art that the invention is not so limited but that various changes may be made therein without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. A rotor blade comprising a beam-like structure disposed interiorly of the contours of the blade, said beam-like structure including a pair of. beam flange portions formed of relatively strong wood and extending from the root of said blade in spaced relation, one of said pair extending along the entire leading edge and the other of said pair extending along the trailing edge portion of said blade and terminating at approximately the mid span of the blade, a beam web portion formed of relatively strong wood interconnecting said flange portions, and filler members formed of relatively light weight wood cemented to said beam-like structure and shaped to define the exterior surfaces of said blade.

2. A rotor blade as claimed in claim 1 including a plywood plate overlapping the junctures between said strong wood beam flange portions and said filler members.

3. A rotor blade as claimed in claim 1 including a glass fabric covering cemented over the composite structure.

4. A rotor blade as claimed in claim 1 wherein said beam flange portions are in slde-by-side connected relation at the root end of said blade but in spaced relation throughout the major spanwise extent thereof.

5. A rotor blade as claimed in claim 1 wherein the beam flange portion extending along the leading edge comprises a laminated birch wood structure and wherein the beam flange portion extending along the trailing edge comprises a laminated spruce wood structure.

6. A rotor blade as claimed in claim 5 including a glass fabric covering cemented over the composite. structure.

CHARLES M. SEIBEL.

REFERENCES CITED y The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,056,592 Siddeey et al Oct. 6, 1936 2,152,861 Bennett Apr. 4, 1939 2,303,707 Pullin Dec. 1, 1942 2,312,219 Sensenich Feb, 23, 1943 2,420,174 Hunt May 6, 1947 2,426,121 Sikorsky Aug. 19, 1947 2,414,125 Rheinfrank Jan. 14, 1947 FOREIGNPATENTS Number Country Date 132,849 Great Britain Sept. 22, 1919 

